As a construction machine represented by a hydraulic excavator, there has been known the one in which the delivery displacement of a variable displacement type hydraulic pump, which serves as a hydraulic source, can be variably controlled so that load pressures of a plurality of hydraulic actuators (namely, various hydraulic cylinders of a working mechanism and hydraulic motors for revolving or traveling) can be load sensed and the pressurized oil can be supplied to the hydraulic actuators in a flow rate corresponding to the load pressures (Patent Document 1).
In addition, as an engine serving as a prime mover of the construction machine, a diesel engine is generally used. In an exhaust gas discharged from the diesel engine, there may be present a harmful substance containing, for example, particulate matter (PM) or nitrogen oxides (NOx). Therefore, in the construction machine represented by a hydraulic excavator, an exhaust gas purifying device is provided in an exhaust pipe constituting an exhaust gas passage of the engine.
The exhaust gas purifying device is provided with an aftertreatment device composed of an oxidation catalyst (generally called “Diesel Oxidation Catalyst” or “DOC” for short) which oxidizes and removes nitrogen monoxide (NO), carbon monoxide (CO) and hydrocarbon (HC) contained in the exhaust gas and a particulate matter removing filter (generally called “Diesel Particulate Filter” or “DPF” for short) which is disposed downstream of the oxidation catalyst to collect and remove particulate matter in the exhaust gas (Patent Document 2).
When a large amount of particulate matter in the exhaust gas is collected by and adhered to the particulate matter removing filter, the filter has to be subjected to a regeneration process. In this case, in nitrogen dioxides (NO2) region, the particulate matter can be burned with the exhaust gas at a temperature as high as 250 to 300 degrees or more, for example. Thus, the particulate matter can be removed from the particulate matter removing filter, achieving the regeneration of the filter.